Dr Kirsten Tillisch, at University of California, Los Angeles, told me: “If we change the bacteria can we change the way we respond?

But she says we need far bigger studies that really probe what species, and even sub-species, of bacteria may be exerting an effect on the brain and what products they are making in the gut.

Dr Tillisch said: “There’s clearly connections here, I think our enthusiasm and our excitement is there because we haven’t had great treatments.

“It’s very exciting to think there’s a whole new pathway that we can study, and we can look and we can help people, maybe even prevent disease.”

And that’s the powerful idea here.

The microbiome – our second genome – is opening an entirely new way of doing medicine and its role is being investigated in nearly every disease you can imagine including allergies, cancer and obesity.

I’ve been struck by how malleable the second genome is and how that is in such stark contrast to our own DNA.

The food we eat, the pets we have, the drugs we take, how we’re born… all alter our microbial inhabitants.

And if we’re doing that unwittingly, imagine the potential of being able to change our microbiome for the better.

Prof Cryan said: “I predict in the next five years when you go to your doctor for your cholesterol testing etc, you’ll also get your microbiome assessed.